The present invention relates to a fluorescent substance excellent in light emission, a method of preparing the fluorescent substance, a fluorescent composition such as, for example, an inking medium for use in an ink jet printer, containing the fluorescent substance, a fluorescent mark carrier such as, for example, postal envelopes, postal cards or postal parcels having a fluorescent mark formed by printing the fluorescent composition, and an optical reader and an optical reading system both operable to optically read the fluorescent mark at a high speed.
(Prior Art 1)
In various fields of industries including the distribution industry, bar codes are widely utilized to control the physical distribution of commodities. The bar codes are also utilized having been printed on various cards such as, for example, pre-paid cards, commutation cards and data cards. These bar codes are read by an optical reader such as, for example, an optical scanner which subsequently processes information represented by the bar codes. Most bar codes carried by surfaces of commodities or cards are in the form of a pattern of stripes printed by the use of a black inking medium against a white background and visible to human eyes under visible rays of light. This visible mark is printed directly on merchandise or printed on a shaped sheet-like carrier which is in turn affixed to merchandise.
On the other hand, attempts have been made to form a mark such as a bar code by the use of a fluorescent substance capable of emitting an infrared region of light so that the fluorescent mark can be identified by an optical reader. While the fluorescent mark is generally invisible to the human eyes, the fluorescent mark emits a fluorescent light when the fluorescent substance contained therein is excited upon irradiation of an external light of a particular wavelength and, therefore, by analyzing the fluorescent light with an optical reader, information represented by the fluorescent mark can be decoded or identified. Even the fluorescent mark is, as is the case with the visible mark, printed directly on merchandise or printed on a shaped sheet-like carrier which is in turn affixed to merchandise.
As compared with the system in which change in intensity of light reflected from the visible mark is read in handling merchandise, a system for handling merchandise, including an optical reader for reading the fluorescent mark, has numerous advantages, some of which are listed below.
(1) Reading of the fluorescent mark is seldom affected adversely by the color of the merchandise and, therefore, the reliability in reading the fluorescent mark is high with the reading error minimized.
(2) Even though the surface on which the fluorescent mark is formed becomes dirty, infrared rays of light emitted from the fluorescent mark has such a long wavelength that the reading error would seldom occur and the reliability is therefore high.
(3) Since the fluorescent substance is substantially colorless under visible rays of light, printing of the fluorescent mark on the merchandise will bring no adverse effect on the aesthetic appearance of the merchandise.
(4) Since the fluorescent substance is so invisible under visible rays of light that no one can recognize the presence of the fluorescent substance, it can provide security of information.
Particulars of interest in this connection are disclosed in, for example, the Japanese Patent Publications No. 55-33837, No. 60-29996 and No. 62-24024.
(Prior Art 2)
The fluorescent mark discussed above is formed by printing a fluorescent inking medium containing a fluorescent substance on a carrier such as, for example, a surface of the merchandise in a predetermined pattern. An infrared fluorescent inking medium has long been known and is disclosed in, for example, the U.S. Pat. No. 4,202,491. The infrared fluorescent inking medium disclosed therein is prepared from an inorganic fluorescent substance containing one or a mixture of neodymium (Nd), ytterbium (Yb) and erbium (Er). The inorganic fluorescent substance which utilizes Nd as an optically active element is known to emit a fluorescent light having a maximum intensity at about 1,050 nm in wavelength when irradiated with an exciting light of 800 nm emitted by a GaAlAs light emitting diode. The inorganic fluorescent substance containing a mixture of Nb and Yb as an optically active element is known to emit a fluorescent light having a maximum intensity at about 980 nm in wavelength when irradiated with an exciting light of 800 nm emitted by a GaAlAs light emitting diode. Similarly, the inorganic fluorescent substance containing a mixture of Yb and Er as an optically active element is known to emit a fluorescent light having a maximum intensity at about 1,050 nm in wavelength when irradiated with an exciting light of 940 nm emitted by a GaAs light emitting diode, and the inorganic fluorescent substance containing a mixture of Nd, Yb and Er as an optically active element is known to emit a fluorescent light having a maximum intensity at about 1,050 nm in wavelength when irradiated with an exciting light of 800 nm emitted by a GaAlAs light emitting diode.
(Prior Art 3)
The fluorescent substance disclosed in, for example, the Japanese Patent Publication No. 56-4598 makes use as the optically active element of Nd having a high absorption characteristic with respect to the infrared region of light, in combination with a fluorescent material capable of exhibiting a high intensity of light emission such as, for example, an alkaline metal salt (for example, Na2MoO4 or the like) which is material for the matrix having a high efficiency of transmission of exciting energies from the optically active element to the emission center, or Yb having an emission center capable of favorably matching in wavelength with a Si photodetector.
(Prior Art 4)
For example, the Japanese Patent Publications No. 54-22326 and No. 61-18231 disclose a method of detecting the presence or absence of the fluorescent mark. In this known method, the fluorescent mark is prepared by the use of a fluorescent substance which emits a fluorescent light when irradiated with an exciting light within the infrared region of wavelength. This known method utilizes the difference between the center wavelength of the exciting light projected onto the fluorescent mark and that of the fluorescent light emitted from the fluorescent substance as a result of the irradiation of the exciting light and, for this purpose, only the fluorescent light is separated by an optical filter from rays of light reflected from the fluorescent mark so that the presence or absence of the fluorescent mark can be eventually detected.
The applicant has suggested a method of and an apparatus for detecting the position of a fluorescent mark by intermittently irradiating the fluorescent marking with the exciting light and then detecting the presence or absence of afterglow emitted from the fluorescent marking during the intermission of irradiation of the exciting light. (See, for example, the Japanese Laid-open Patent Publication No. 5-20512.)
(Prior Art 5)
FIG. 70 illustrates the prior art optical reading apparatus. The fluorescent mark shown therein is in the form of a fluorescent bar code 401 comprised of a pattern of parallel bars formed by printing the fluorescent inking medium on a sheet-like carrier 404 such as, for example, a label. The fluorescent inking medium used to form the bar code 401 contains fluorescent microparticles dispersed and retained in a binder, said fluorescent microparticles being of a kind which emit, when excited by an exciting light of a particular wavelength, for example, infrared rays of light 402, a fluorescent light 403 of a wavelength different from that of the infrared rays of light 402.
An optical reading apparatus for reading information from the fluorescent bar code 401 includes a light emitter 405 for emitting the infrared rays of light 402, a light receiver 407 for detecting the fluorescent light 403 from the bar code 401 and rays of light 406 reflected from the carrier 404 and for converting them into an electric signal, an amplifier 408 for amplifying the electric signal and for outputting an analog reproduction signal, and a signal detector 409 for detecting from the analog reproduction signal of the amplifier 408 information represented by the bar code 401. The signal detector 409 used therein includes an analog-to-digital (A/D) converter which is operable to digitize the analog reproduction signal so that the information represented by the fluorescent bar code 401 can be reproduced.
For digitization of the analog reproduction signal, a comparator is generally utilized, having an input stage which is adapted to receive the analog reproduction signal A and a slice signal B of a predetermined level shown in FIG. 66 so that the analog reproduction signal A can be sliced by the slice signal B to provide a digitized signal.
(Problem 1)
In the various fluorescent substances and the various fluorescent marks formed by printing the fluorescent inking media containing the respective fluorescent substances, both having hitherto been suggested, neither the relationship between the particle size of the particular fluorescent substance and the wavelength of the exciting light used nor the relationship between the particle size of the particular fluorescent substance and the wavelength of the fluorescent light emitted by such particular fluorescent substance has been taken into consideration. The conventional fluorescent substance has a particle size as relatively large as 5 to 6 xcexcm. On the other hand, for a light source for exciting the fluorescent substance, a semiconductor laser, for example, is generally utilized, capable of emitting a laser beam of about 0.8 xcexcm in wavelength while the fluorescent light emitted from the conventional fluorescent substance has a wavelength of about 1 xcexcm.
As discussed above, the conventional fluorescent particles have a relatively great particle size, i.e., a particle size as great as about 5 to 7.5 times the wavelength of any one of the exciting light and the fluorescent light. For this reason, if the fluorescent mar is prepared by the use of the fluorescent inking medium containing the fluorescent particles of that particle size, the fluorescent particles are deposited in such an overlapping relation that the exciting light projected towards a deposit of the fluorescent inking medium will not reach some of the fluorescent particles at a deep region of the deposit of the fluorescent inking medium, and for this reason, the efficiency of activation (excitation) of the fluorescent substance is lowered.
Even if some of the fluorescent particles at the deep region of the deposit of the fluorescent inking medium are excited to emit a fluorescent light, the fluorescent light so emitted tends to be partly intercepted by other fluorescent particles residing over such some of the fluorescent particles within the deposit of the inking medium, with the intensity of the fluorescent light consequently lowered. Consequently, the fluorescent light of such a low intensity often creates a problem associated with the reliability in detecting the presence or absence of the fluorescent mark.
Thus, partly because the efficiency of activation (excitation) of the fluorescent substance is low and partly because part of the fluorescent light excited will not emerges outwardly from an exterior surface of the deposit of the fluorescent inking medium and, hence, the intensity of the fluorescent light is consequently low, the prior art fluorescent substance poses a problem associated with the reliability in detecting the presence or absence of the fluorescent mark.
(Problem 2)
The fluorescent substance generally has such a property that when irradiated with the exciting light the fluorescent substance is activated to emit a fluorescent light in a progressively increasing quantity, but in the absence of the exciting light the quantity of the fluorescent light emitted decreases progressively. With the conventional fluorescent substance, the length of time, that is, the rise time, which passes from the start of irradiation of the exciting light upon the fluorescent substance and until the resultant fluorescent light attains a desired intensity is long. For this reason, a high velocity of movement of the fluorescent mark carrier relative to the optical reader cannot be employed, constituting an obstruction to the use of a high speed optical reader. If the relative velocity is increased, information represented by the fluorescent mark will no longer be read accurately and properly.
Although this is related to the relatively long rise time of the fluorescent light referred to above, the conventional fluorescent substance has a length of time (that is, the fall time) which passes from the interruption of irradiation of the exciting light upon the fluorescent substance and until the intensity of the fluorescent afterglow attains zero, that is, until the fluorescent light is no longer detected is long as well. For this reason, where the fluorescent mark consists of a plurality of parallel fluorescent bars, reduction in spacing between each neighboring fluorescent bars will render the light receiving element to detect a fluorescent afterglow emanating from the adjoining fluorescent bar, failing to provide an accurate information reading.
(Problem 3)
Inorganic powdery fluorescent pigments such as Nd, Yb and Er discussed hereinbefore have a relatively large particle size. Although this particle size would pose no problem if the fluorescent particles are tramped down with resin before use, the use of the fluorescent pigment of a relatively large particle size in an inking medium for use with an ink jet printer would, unless the particle size is reduced, result neither in a homogenous and beautiful print, nor in a high resolution during information reading. On the other hand, if the fluorescent particles are finely pulverized with the use of a mill, the fluorescent output would eventually decrease considerably.
The inventors of the present invention have also found that, in addition to the above discussed problems, the inorganic fluorescent pigments bring about an additional problem in that the response of the fluorescent substance to emit the fluorescent light subsequent to receipt of the exciting light is so low that a high speed reading is difficult to achieve.
(Problem 4)
In the Japanese Patent Publication No. 56-4598 referred to above, there is disclosed that the matrix material of the infrared-excitable fluorescent substance contains alkaline metal cations, Li+Na+, if an anion thereof is chosen MoO22xe2x88x92 or Wo42xe2x88x92. Since a salt of alkaline metal which is generally a monovalent metal has a relatively weak bond between the anion and the cation because of a small valence sufficient to be easily released to form a hydrate, the alkaline metal salt is water-soluble. Accordingly, the fluorescent substance prepared from the alkaline metal salt as a matrix material is extremely poor in water resistance to such an extent as to result in an obnoxious problem in practical use.
The infrared-excitable fluorescent substance is prepared by weighing, mixing and pressure-forming only the starting materials (for example, Na2CO3, MoO3, Nd2O3 and Yb2O3), incinerating the preformed mixture and subsequently mechanically pulverizing it to provide the powdery fluorescent substance. In such case, the resultant fluorescent particles have a minimum particle size as small as about 5 xcexcm. Although this particle size permits the fluorescent particles to be used as a material for a printing ink medium such as used in, for example, a screen printing technique, the fluorescent particles of this particle size cannot be used as a material for an inking medium for use with an ink jet printer or for use in an inked ribbon. This is because the inking medium for use in the practice of a printing technique requires the fluorescent substance of 1 xcexcm or smaller in particle size, the fluorescent substance of about 5 xcexcm in particle size is not suited as a material for the inking medium that is used with the ink jet printer or in the inked ribbon.
The Japanese Laid-open Patent Publication No. 5-261634 referred to above discloses that the fluorescent substance having its matrix material in the form of a salt of PO4 and activated by Nd and Yb can be used in an inking medium for use in an offset printing technique provided that such fluorescent substance is pulverized to a particle size within the range of 0.1 to 3 xcexcm.
However, the infrared-excitable fluorescent substance of this system has been found that both of the rise time, required for it to emit a fluorescent light of the maximum intensity subsequent to irradiation of infrared rays of light, and the fall time required for the intensity of the fluorescent light to attain zero subsequent to interruption of the infrared irradiation are extremely long, and therefore, it cannot satisfactorily be used where the exciting light is in the form of a pulsating light of short duration and/or where a high speed reading with, for example, a high speed scanner is desired.
The inventors of the present invention, in an attempt to develop an infrared-excitable fluorescent substance having a high response, have examined the use of Na2MoO4 as a matrix of the infrared-excitable fluorescent substance, but have found that, because Na2MoO4 is water-soluble, the fluorescent substance having its matrix added with optically active elements has exhibited a poor water resistance. Also, the fluorescent substance obtained had a particle size greater than a few microns and have therefore been found not suited for use as a material for the ink jet printer or the inked ribbon or in a printing technique such as an offset printing process.
(Problem 5)
Hitherto, in preparing a fluorescent composition such as, for example, the inking medium for use with an ink jet printer and containing fluorescent particles, none of the particle size of the fluorescent substance used, the density of the fluorescent substance and/or the density of a binder used, and the relationship among viscosity, surface tension, specific resistance and pH value has not taken into consideration. For this reason, the fluorescent particles contained in the fluorescent composition have such problems that the fluorescent particles are apt to sediment in the fluorescent composition, exhibiting an unsatisfactory dispersion stability, that the fluorescent composition tends to run during the printing and/or that the fluorescent output is low.
(Problem 6)
In the prior art fluorescent inking medium containing the fluorescent particles, the fluorescent substance is employed in a quantity generally within the range of 30 to 85 wt % relative to the total weight of the inking medium and is in the form of an inorganic compound having a relatively large particle size as discussed hereinabove. The use of the fluorescent substance in such a large quantity brings about such a problem that a fluorescent ink deposit formed by printing the fluorescent inking medium is so raised as to provide a visible indication of the presence of the ink deposit. This is problematic in terms of security particularly when a fluorescent mark is desired to be formed by depositing the inking medium at a location where the ink deposit will not constitute any obstruction to the eyes.
(Problem 7)
With respect to the fluorescent ink deposit formed by the use of the conventional fluorescent inking medium containing the fluorescent particles, no surface roughness of the ink deposit has been studied. Since the fluorescent substance of the relatively large particle size as discussed above has been employed, the surface of the ink deposit is relatively rough, having minute surface irregularities. Irradiation of the exciting light upon the rough-surfaced ink deposit tends to result in scattering of the exciting light upon the surface of the ink deposit, accompanying reduction in quantity of the exciting light penetrating into the fluorescent ink deposit. Also, with the rough-surfaced ink deposit, the fluorescent light emitted internally from the fluorescent ink deposit is apt to scatter in all directions at the surface of the ink deposit and, therefore, the quantity of the fluorescent light received by a light receiving element may be reduced correspondingly.
Once the above discussed phenomenon occurs, an output generated from the light receiving element in response to detection of the fluorescent light emitted from the fluorescent ink deposit is so low as to bring about a problem associated with the reliability in detecting the presence or absence of the fluorescent mark.
(Problem 8)
An optical reading apparatus used in connection with the fluorescent mark is known and includes a semitransparent mirror disposed generally intermediate between the fluorescent mark to be detected and a photoelectric detector assembly inclusive of light emitting and receiving elements. The known optical reading apparatus is so structured that the exciting light emitted from the light emitting element may be projected through the semitransparent mirror onto the fluorescent mark carrier so that the fluorescent light emitted from the fluorescent mark on the carrier can pass through the same semitransparent mirror before it is detected by the light receiving element. With this structure, it has been observed that as the exciting light travels through the semitransparent mirror, generally half of the exciting light may be reflected in direction other than the direction towards the fluorescent mark carrier and/or that as the fluorescent light emitted from the fluorescent mark on the carrier travels through the semitransparent mirror, generally half of the fluorescent light may be reflected in directions other than the direction towards the light receiving element. For this reason, the quantity of the exciting light necessary to activate the fluorescent substance is in practice small and, hence, the quantity of the fluorescent light emitted is correspondingly small and, yet, the light receiving element receives the fluorescent light in a quantity generally half of the actually emitted fluorescent light. Therefore, the light receiving element issues a considerably low output, so low as to bring about a problem associated with the reliability in detecting the fluorescent mark.
(Problem 9)
In the prior art optical reading apparatus, the exciting light emitted from the light emitting element forms a round irradiating pattern of a size sufficient to encompass the size of the bar code forming the fluorescent mark. Irradiation of the round light spot upon the fluorescent mark does not affords a sufficient area of surface to be illuminated and the intensity of the fluorescent light emitted from the fluorescent mark is consequently low. If an attempt is made to increase the size of the round light spot to thereby increase the area of surface to be illuminated, the exciting light will encompass not only the bar code of interest, but also the bar code adjoining such bar code of interest. This in turn brings about reduction in S/N (signal-to-noise) ratio, accompanying a problem associated with the reliability in detecting the fluorescent mark.
(Problem 10)
In designing the prior art optical reading apparatus, neither the rise time of the fluorescent light subsequent to irradiation of the exciting light, nor the relationship between the width of a slit extending in a direction of transport of the fluorescent mark carrier and the speed of transport of the fluorescent mark carrier is taken into consideration.
Also, neither the fall time of the fluorescent light subsequent to interruption of the exciting light, nor the relationship between the interval between the neighboring bars of the fluorescent mark (i.e., the fluorescent bar code) and the speed of transport of the fluorescent mark carrier is taken into consideration.
Because of the foregoing, no information represented by the fluorescent ink deposit on the fluorescent mark carrier can be read.
(Problem 11)
In the prior art optical reading apparatus, a slit member is interposed between the sheet-like fluorescent mark carrier such as, for example, a paper, and an object lens assembly so that only that portion of the fluorescent light emitted from the fluorescent mark which is desired to be detected is received by the light receiving element through the slit in the slit member. Although this will bring about no problem if the fluorescent mark carrier has a substantially uniform thickness, there is a problem in that, if the fluorescent mark carrier having a relatively great, but irregular thickness is transported, the fluorescent mark carrier being transported may be blocked with its front engaged with the slit and/or the slit will be damaged.
(Problem 12)
The prior art method of detecting the mark such as disclosed in the Japanese Patent Publications No. 54-22326 and No. 61-18231 and the Japanese Laid-open Patent Publications No. 3-16369 and No. 5-20512 all referred to above, is such that the fluorescent light emitted from the fluorescent mark as a result of excitation by the exciting light is detected by a detector. However, the quantity of the fluorescent light incident on the detector considerably varied with change in environments and conditions in and under which the detection is performed and, therefore, in order to secure a high accuracy of detection, a complicated circuit processing is required, or the condition of use is limited.
As a result of studies conducted by the inventors of the present invention in view of the foregoing problems, it has been found that any one of the prior art detecting method is unable to properly and accurately monitor the change in detecting condition because of an insufficient quantity of information available other than data associated with the fluorescent mark.
(Problem 13)
In another prior art method in which an optical filter used to separate the exciting light, which has been reflected, and the fluorescent light from each other, since the wavelength of the emission center of the reflected exciting light and that of the fluorescent light are close to each other and the intensity of the fluorescent light is extremely low as compared with that of the reflected exciting light, the both cannot be properly separated from each other with no difficulty and, in a certain case, most of the reflected exciting light may remain unseparated and enter the light receiving element together with the fluorescent light. Once this occurs, the accuracy of detection is lowered.
(Problem 14)
According to the fluorescent mark detecting method disclosed in, for example, the Japanese Laid-open Patent Publications No. 3-16369 and No. 5-20512 referred to above, if external rays of light of a wavelength matching with or in the vicinity of the wavelength of the fluorescent light exist in the environment in which the fluorescent light is being detected, such rays of light may be sensed by and converted into an electric output by the light receiving element. This leads to generation of false information that, even though no fluorescent light has yet been emitted, the fluorescent light was detected. In order to avoid such false information, both of the site of emission of the exciting light and the site of detection of the fluorescent light are required to be shielded from the external light, thus limiting the environment in which the system is used.
(Problem 15)
In the optical reading apparatus of a structure shown in FIG. 71, both of the level and the amplitude of the analog reproduction signal discussed hereinbefore are considerably affected by physical surface properties of the carrier on which the bar code is formed in the form of the fluorescent mark. More specifically, where the surface of the carrier is made of material having a propensity of absorbing a transparent inking medium and also the exciting light projected from an illuminator unit, the quantity of the fluorescent light emitted from the fluorescent bar code and the quantity of light reflected from the carrier are so small that, as shown in FIG. 71(b), the analog reproduction signal exhibits a low level and a low amplitude.
Also, where the carrier is made of material having a propensity of absorbing the transparent inking medium and also that of reflecting the light projected by the illuminator unit, the analog reproduction signal is apt to offset towards a high level as shown in FIG. 71(c). Moreover, where the carrier is made of material having a propensity of absorbing little transparent inking medium, but absorbing the light projected by the illuminator unit, the analog reproduction signal exhibits an increased amplitude as shown in FIG. 71(a).
Accordingly, with the prior art reading apparatus in which variation in waveform of the analog reproduction signal resulting from difference in type of the carriers on which the fluorescent bar codes are formed is taken into consideration, when the single reading apparatus is used to read one at a time the fluorescent bar codes formed on, for example, the respective carriers made of different materials, or when the reading apparatus is used to read one at a time the fluorescent bar codes formed on different portions of the single carrier which are made of varying materials, a problem is apt to occur in that the bar codes will not be accurately read. This problem may be avoided if an optical filter (a single wavelength filter) operable to cut off the entire light reflected from the carrier is disposed in front of the light receiving element. However, the single wavelength filter is expensive and cannot, in terms of cost, be installed in the optical reading apparatus and, instead, the above discussed problem does often occur since a band-pass filter operable to cut off a portion of the reflected light is generally employed.
Accordingly, a primary object of the present invention is to provide a highly reliable fluorescent substance having a high emissive output, a fluorescent composition, a fluorescent mark carrier, an optical reading apparatus, a merchandise sorting apparatus and a merchandise sorting system all of which are effective to substantially eliminate the above discussed problems inherent in the prior art.
Another important object of the present invention is to provide the fluorescent substance and the fluorescent composition which are effective to substantially eliminate the above discussed problems inherent in the prior art, excellent in durability, fine in particle size suitable for use in various printing techniques such as those employing an ink jet printer or an inked ribbon, and capable of exhibiting a high response.
A further important object of the present invention is to provide an optically detectable mark effective to substantially eliminate the above discussed problems inherent in the prior art and with which change in environmental conditions in which data are being detected can be readily and properly determined.
A still further important object of the present invention is to provide a detecting method and an optical reading apparatus effective to substantially eliminate the above discussed problems inherent in the prior art and capable of accomplishing accurate detection of the position at which the mark is formed, regardless of deterioration in condition in which the fluorescent light emitted from the mark is detected.
A yet further important object of the present invention is to provide the optical reading apparatus effective to substantially eliminate the above discussed problems inherent in the prior art and capable of accomplishing assured detection of the fluorescent mark without being adversely affected by environments in which it is used.
A different important object of the present invention is to provide the reading apparatus effective to substantially eliminate the above discussed problems inherent in the prior art and capable of accurately reading the fluorescent light at all times with no need to use the expensive single wavelength filter and regardless of the waveform of the analog reproduction signal.
The first invention is directed to the fluorescent substance of a kind capable of emitting, in response to irradiation of the exciting light, a fluorescent light of a wavelength different from that of the exciting light and is characterized in that, in order to accomplish the foregoing objects, the average particle size of the fluorescent substance being of super microparticles is smaller than the maximum intensity of the fluorescent light emitted by such fluorescent substance.
The second invention is directed to the fluorescent substance of a kind capable of emitting, in response to irradiation of the exciting light, a fluorescent light of a wavelength different from that of the exciting light and is characterized in that, in order to accomplish the foregoing objects, the average particle size of the fluorescent substance being of ultra-microparticles is smaller than the maximum intensity of the exciting light.
The fluorescent substance according to the third invention is characterized in that, in order to accomplish the foregoing objects, it comprises a salt of oxyacid containing at least one optical active element selected from the group consisting of Nd, Yb and Er, said salt of oxyacid being expressed by, for example, the following general formula (1) or (2):
LnxA1xe2x88x92XPO4xe2x80x83xe2x80x83(1) 
wherein:
Ln represents at least one element selected from the group consisting of Nd, Yb and Er;
A represents at least one element selected from the group consisting of Y, La, Gd, Bi, Ce, Lu, In and Tb; and
X represents a value within the range of 0.01 to 0.99.
DE1xe2x88x92XLnXPYOZxe2x80x83xe2x80x83(2) 
wherein:
D represents at least one element selected from the group consisting of Li, Na, K, Rb and Cs;
E represents at least one element selected from the group consisting of Y, La, Gd, Bi, Ce, Lu, In and Tb;
Ln represents at least one element selected from the group consisting of Nd, Yb and Er;
X represents a value within the range of 0.01 to 0.99;
Y represents a value within the range of 1 to 5; and
Z represents a value within the range of 4 to 14.
The fluorescent substance according to the fourth invention is characterized in that, in order to accomplish the foregoing objects, it comprises Fe and Er, both as an optical active element, and, other than these optical active elements, at least one element selected from the group consisting of Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La and is expressed by one of the following general formulas (3), (4) and (5):
wherein:
G represents at least one element selected from the group consisting of Y, Bi, Ce, Gd, Lu and La, and Er; and
J represents at least one element selected from the group consisting of Sc, Ga, Al and In, and Fe.
The fluorescent substance according to the fifth invention is characterized in that, in order to accomplish the foregoing objects, it comprises Yb as an optical active element and, other than that optical active element, at least one element selected from the group consisting of Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La and is expressed by one of the following general formulas (6), (7) and (8):
wherein:
L represents at least one element selected from the group consisting of Y, Bi, Ce, Gd, Lu and La, and Yb; and
M represents at least one element selected from the group consisting of Sc, Ga, Al and In.
The fluorescent substance according to the sixth invention is characterized in that, in order to accomplish the foregoing objects, it comprises at least one organic substance containing a rare earth element, said rare earth element being selected from the group consisting of Nd, Yb and/or Er, is combined with at least one organic substance such as, for example, polymethine, anthraquinone, dithiol metal, phthalocyanine, indophenol or azo dyestuff of a kind having an absorption band within the infrared region of rays of light.
The seventh invention is characterized in that, in order to accomplish the foregoing objects, it contains at least one of Nd and Yb as an optical active element and, other than this optical active element, at least one oxide of Mo or W and an alkaline earth metal and is expressed by one of the following general formulas (9) and (10):
(Nd1xe2x88x92XYbX)YQZ(RO4)xe2x80x83xe2x80x83(9) 
wherein:
Q represents at least one element selected from the group consisting of Ca, Mg, Sr and Ba;
R represents at least one element selected from the group Mo and W;
X represents a value within the range of 0 to 1;
Y represents a value greater than 0, but smaller than 1; and
Z represents a value greater than 0, but smaller than 1.
(Nd1xe2x88x92XYbX)2YQ8xe2x88x923Y(RO4)8xe2x80x83xe2x80x83(10) 
wherein:
Q represents at least one element selected from the group consisting of Ca, Mg, Sr and Ba;
R represents at least one element selected from the group Mo and W;
X represents a value within the range of 0 to 1; and
Y represents a value greater than 0, but equal to or smaller than 8/3.
A method of preparing the fluorescent substance according to the eighth invention is characterized in that, in order to accomplish the foregoing objects, at least one optical active element selected from the group consisting of Nd and Yb, at least one oxide of one of Mo and W and an alkaline earth metal are added to a flux material containing a salt expressed by T2RO4.nH2O (wherein T is at least one element selected from the group consisting of Li, Na and K, R is at least one element selected from the group consisting of Mo and W, and n is a value greater than 0) which is subsequently calcinated, followed by dissolution of the incinerated product with the use of a solvent to remove the flux material.
The fluorescent composition according to the ninth invention is characterized in that, in order to accomplish the foregoing objects, it comprises a fluorescent substance in the form of ultra-microparticles capable of emitting a fluorescent light of a wavelength different from that of the exciting light and having an average particle size smaller than the wavelength of the maximum intensity of the fluorescent light, a binder transparent to both of the exciting light and the fluorescent light, and a solvent.
The fluorescent composition according to the tenth invention is characterized in that, in order to accomplish the foregoing objects, it comprises a fluorescent substance in the form of ultra-microparticles capable of emitting a fluorescent light of a wavelength different from that of the exciting light and having an average particle size smaller than the wavelength of the maximum intensity of the exciting light, a binder transparent to both of the exciting light and the fluorescent light, and a solvent.
The fluorescent composition according to the eleventh invention is characterized in that, in order to accomplish the foregoing objects, it comprises a fluorescent substance containing at least one organic substance which contains a rare earth element and which is selected from the group consisting of Nb, Yb and/or Er, and is combined with at least one organic substance having at least one absorption band within the infrared region of light, and an organic binder.
The fluorescent composition according to the twelfth invention is characterized in that, in order to accomplish the foregoing objects, it comprises a fluorescent substance containing at least one of Nd and Yb as an optical active element and, other than this optical active element, at least one oxide of one of Mo and W and an alkaline earth metal, and an organic binder.
The inked ribbon according to the thirteenth invention is characterized in that, in order to accomplish the foregoing object, it comprises a tape-like carrier deposited with the fluorescent composition comprising a fluorescent substance containing at least one of Nd and Yb as an optical active element and, other than this optical active element, at least one oxide of one of Mo and W and an alkaline earth metal, which fluorescent substance is dispersed and retained in a organic binder.
The fluorescent mark carrier according to the fourteenth invention is characterized in that, in order to accomplish the foregoing objects, the fluorescent mark containing the fluorescent substance in the form of ultra-microparticles capable of emitting a fluorescent light of a wavelength different from that of the exciting light and having an average particle size smaller than the wavelength of the maximum intensity of the fluorescent light is printed thereon.
The fluorescent mark carrier according to the fifteenth invention is characterized in that, in order to accomplish the foregoing objects, the fluorescent mark containing the fluorescent substance in the form of ultra-microparticles capable of emitting a fluorescent light of a wavelength different from that of the exciting light and having an average particle size smaller than the wavelength of the maximum intensity of the exciting light is printed thereon.
In order to accomplish the foregoing objects, the sixteenth invention is characterized by a fluorescent mark carrier printed with a fluorescent mark containing fluorescent particles capable of emitting a fluorescent light of a wavelength different from that of the exciting light, the content of said fluorescent particles in the fluorescent mark being greater than 1 wt %, but smaller than 30 wt %.
In order to accomplish the foregoing objects, the seventeenth invention is characterized by the fluorescent mark carrier printed with a fluorescent mark containing fluorescent particles capable of emitting a fluorescent light of a wavelength different from that of the exciting light, a deposit of the fluorescent inking medium having a thickness not greater than 35 times the particle size of the fluorescent particles.
In order to accomplish the foregoing objects, the eighteenth invention is characterized by the fluorescent mark carrier printed with a fluorescent mark containing fluorescent particles capable of emitting a fluorescent light of a wavelength different from that of the exciting light and a binder, said binder having a light transmissivity with respect to each of the exciting and fluorescent light being not lower than 80%.
In order to accomplish the foregoing objects, the fluorescent mark carrier according to the nineteenth invention is characterized in that the fluorescent particles capable of emitting a fluorescent light of a wavelength different from that of the exciting light are deposited on an aggregation of fibers.
In order to accomplish the foregoing objects, the fluorescent mark carrier according to the twentieth invention is characterized in that a fluorescent ink deposit containing the fluorescent substance capable of emitting a fluorescent light of a wavelength different from that of the exciting light has a 20% or lower visible ray absorption characteristic.
In order to accomplish the foregoing objects, the twenty-first invention is directed to an optical reading apparatus comprising a light emitting element for irradiating with the exciting light a fluorescent mark carrier carrying a fluorescent mark containing the fluorescent substance, a mirror for reflecting light from the fluorescent substance and a light receiving element for receiving the light reflected by the mirror, which apparatus is characterized in that the mirror has a portion thereof provided with a light transmitting region such as, for example, a perforation, for allowing a substantially entire quantity of the exciting light from the light emitting element to pass therethrough and is in the form of a total reflecting mirror such as, for example, a front surfaced mirror, having a reflectivity of higher than 50%.
In order to accomplish the foregoing objects, the twenty-second invention is directed to an optical reading apparatus comprising a light emitting element for irradiating with the exciting light a fluorescent mark carrier carrying a bar code containing the fluorescent substance, and a light receiving element for receiving light from the fluorescent substance, which apparatus is characterized in that the exciting light is projected in an irradiating pattern of a generally elliptical shape having its major axis extending in a direction lengthwise of the bar code.
In order to accomplish the foregoing objects, the twenty-third invention is directed to an optical reading apparatus comprising a light emitting element for irradiating with the exciting light a fluorescent mark carrier printed with the fluorescent substance, a light receiving element for receiving a fluorescent light from the fluorescent mark carrier, a slit member disposed on an optical path between the light emitting element and the light receiving element, and a transport means for transporting the fluorescent mark carrier in a predetermined direction, which apparatus is characterized in that the transport means transports the fluorescent mark carrier at a velocity v which has the following relationship:
d/vxe2x89xa7tu 
wherein d represents the length of an opening in the slit member as measured in a direction conforming to the direction of transport of the fluorescent mark carrier, v represents the velocity of transport of the fluorescent mark carrier and tu represents the length of time from the timing at which the fluorescent substance receives the exciting light to the timing at which the intensity of the light emitted by the fluorescent substance attains 90% of the maximum possible intensity thereof.
In order to accomplish the foregoing objects, the twenty-fourth invention is directed to an optical reading apparatus comprising a light emitting element for irradiating with the exciting light a fluorescent mark carrier printed with the fluorescent substance, a light receiving element for receiving a fluorescent light from the fluorescent mark carrier and a transport means for transporting the fluorescent mark carrier in a predetermined direction, which apparatus is characterized in that the transport means transports the fluorescent mark carrier at a velocity v which has the following relationship:
L/vxe2x89xa7td 
wherein L represents the interval between neighboring portions printed with the fluorescent substance with respect to the direction of transport, v represents the velocity of transport of the fluorescent mark carrier, and td represents the length of time from the timing at which irradiation of the exciting light is interrupted to the timing at which the fluorescent afterglow attenuates by a quantity corresponding to 80% of the maximum possible intensity thereof.
In order to accomplish the foregoing objects, the twenty-fifth invention provides an optical reading apparatus comprising a light emitting element for irradiating with the exciting light a fluorescent mark carrier carrying the fluorescent substance, a light receiving element for receiving a fluorescent light from the fluorescent mark carrier, a transport means for transporting the fluorescent mark carrier in a predetermined direction, a first convex lens disposed on an optical path from the fluorescent mark carrier to the light receiving element and having a flat surface oriented towards the fluorescent mark carrier, a second convex lens disposed on an optical path from the fluorescent mark carrier to the light receiving element and having a flat surface oriented towards the light receiving element, and a slit member disposed between the second convex lens and the light receiving element.
In order to accomplish the foregoing objects, the twenty-sixth invention is directed to an optical reading apparatus comprising a light emitting element for irradiating with the exciting light a fluorescent mark carrier printed with the fluorescent substance, and a light receiving element for receiving a fluorescent light from the fluorescent mark carrier, characterized in that the light emitting element is a semiconductor laser diode, a drive circuit for driving the semiconductor laser diode having an automatic power control function, and there is provided a hold circuit for monitoring the exciting light emitted from the semiconductor laser diode and holding an output condition of the exciting light such that based on a signal from the hold circuit an output condition of the exciting light from the semiconductor laser diode is controlled by the drive circuit.
In order to accomplish the foregoing objects, a merchandise sorting apparatus according to the twenty-seventh invention is characterized in that the merchandise sorting apparatus comprises a light emitting element for irradiating with the exciting light a fluorescent mark carrier printed with the fluorescent substance, a light emitting element for receiving a fluorescent light from the fluorescent mark carrier, a slit member disposed on an optical path between the light emitting element and the light receiving element, a transport means for transporting the fluorescent mark carrier in a predetermined direction, and a sorting means for sorting the fluorescent mark carrier, in that the length d of an opening in the slit member as measured in a direction conforming to the direction of transport of the fluorescent mark carrier, the velocity v of transport of the fluorescent mark carrier by the transport means, and the length of time tu from the timing at which the fluorescent substance receives the exciting light to the timing at which the intensity of the light emitted by the fluorescent substance attains 90% of the maximum possible intensity thereof have a relationship of (d/vxe2x89xa7tu), and in that information represented by a fluorescent ink deposit provided on the fluorescent mark carrier is read by the exciting light and the fluorescent light passing through a slit formed in the slit member, said fluorescent mark carrier being sorted according to such information.
In order to accomplish the foregoing objects, a merchandise sorting apparatus according to the twenty-eighth invention is characterized in that the merchandise sorting apparatus comprises a light emitting element for irradiating with the exciting light a fluorescent mark carrier printed with the fluorescent substance, a light emitting element for receiving a fluorescent light from the fluorescent mark carrier, a slit member disposed on an optical path between the light emitting element and the light receiving element, a transport means for transporting the fluorescent mark carrier in a predetermined direction, and a sorting means for sorting the fluorescent mark carrier, in that the interval between neighboring portions printed with the fluorescent substance with respect to the direction of transport, the velocity v of transport of the fluorescent mark carrier, and the length of time td from the timing at which irradiation of the exciting light is interrupted to the timing at which the fluorescent afterglow attenuates by a quantity corresponding to 80% of the maximum possible intensity thereof have a relationship of (L/vxe2x89xa7td), and in that information represented by a fluorescent ink deposit provided on the fluorescent mark carrier being transported is optically read and the fluorescent mark carrier is sorted according to such information.
In order to accomplish the foregoing objects, the twenty-ninth invention provides a merchandise sorting apparatus characterized by the provision of an visible image optical reading means for optically reading destination information described on a surface of a merchandise to be sorted, a fluorescent substance printing means for printing the destination information on the merchandise with the use of a fluorescent substance according to the destination information read by the visible image optical reading means, a fluorescent mark optical reading means for optically reading information represented by a fluorescent ink deposit formed by the fluorescent substance printing means, and a sorting means for sorting the merchandise according to the destination information read by the fluorescent mark optical reading means.
In order to accomplish the foregoing objects, the thirtieth invention provides a merchandise sorting method characterized by the steps of optically reading destination information described on a surface of a merchandise with the use of a visible image optical reading means, printing destination information on the merchandise with the use of a fluorescent substance according to the destination information read by the visible image optical reading means, optically reading information represented by a fluorescent ink deposit with the use of a fluorescent mark optical reading means, and sorting the merchandise according to the destination information read by the fluorescent mark optical reading means.
In order to accomplish the foregoing objects, the thirty-first invention provides a mark to be detected containing a fluorescent substance capable of emitting light of a wavelength different from that of an exciting light, which mark is characterized by the provision of a data area formed with a pattern corresponding to data to be recorded, and a lead-in area formed at a site that is scanned prior to irradiation with the exciting light upon the data area, said lead-in area continuing a sufficient length greater than the longest continuous portion of the pattern formed at the data area.
In order to accomplish the foregoing objects, the thirty-second invention provides a method for detecting the mark of the thirty-first invention, characterized in that the method comprises a light irradiating step of projecting light of a substantially constant intensity, an photoelectrically converting step of receiving the light emitted from a light emitting position and converting it into an electric signal, a comparison value setting step of automatically setting a comparison value from an electric signal corresponding to the lead-in area of the mark, and a mark determining step of comparing a detected value corresponding to the data area in the mark with the comparison value and determining, in the event that the detected value exceeds the comparison value, the position at which the mark is formed.
In order to accomplish the foregoing objects, the thirty-third invention provides a method of detecting a mark by irradiating the mark, containing the fluorescent substance, with an exciting light and receiving a fluorescent light emitted from the mark, characterized in that the method comprises a step of intermittently projecting the exciting light of a substantially constant intensity, a step of receiving light, emitted from an irradiating position of the exciting light, and converting it into an electric signal, an incident light intensity detecting step of outputting as a comparison value an electric signal corresponding to the intensity of incident light during an irradiating period, a fluorescent intensity detecting step of outputting, as a detected value, an electric signal indicative of the magnitude of a fluorescent component of the incident light, and a determining step of comparing the detected value with the comparison value and determining, in the event that the detected value exceeds the comparison value, the position at which the mark is formed.
In order to accomplish the foregoing objects, the thirty-fourth invention provides an optical reading apparatus for detecting a mark by irradiating the mark to be detected, containing the fluorescent substance capable of emitting light of a wavelength different from that of an exciting light, with the exciting light and receiving a fluorescent light emitted from the mark, characterized in that it comprises a light irradiating means for projecting the exciting light of a substantially constant intensity intermittently at a predetermined cycle, a photoelectric converting means for receiving the light emitted from a light emitting position and converting it into an electric signal, a waveform detecting means synchronized with an irradiating timing of the light irradiating means for making it possible to individually detect a minimum value shortly before start of the irradiation, a maximum value shortly before interruption of the irradiation and a detected value immediately after interruption of the irradiation, and a mark determining means for comparing the detected value with a comparison value obtained by dividing the difference between the maximum value and the minimum value and for determining, in the event that the detected value exceeds the comparison value, the position at which the mark is formed.
In order to accomplish the foregoing objects, the thirty-fifth invention provides an optical reading apparatus for detecting a mark by irradiating the mark to be detected, containing the fluorescent substance capable of emitting light of a wavelength different from that of an exciting light, with the exciting light and receiving a fluorescent light emitted from the mark, characterized in that it comprises a light irradiating means for projecting the exciting light of a substantially constant intensity intermittently at a predetermined cycle, a photoelectric converting means for receiving the light emitted from a light emitting position and converting it into an electric signal, a waveform shaping means for inverting and amplifying half of an output signal from the photoelectric converting means in synchronism with a timing displaced 90xc2x0 relative to a period of irradiation by the light irradiating means, and a low-pass filtering means for selectively outputting a direct current component from the output signal of the waveform shaping means.
In order to accomplish the foregoing objects, the thirty-sixth invention provides an optical reading apparatus for detecting a mark by irradiating the mark to be detected, containing the fluorescent substance capable of emitting light of a wavelength different from that of an exciting light, with the exciting light and receiving a fluorescent light emitted from the mark, characterized in that it comprises a light irradiating means for projecting the exciting light of a substantially constant intensity intermittently at a predetermined cycle, a filtering means for selectively receiving a component of light emitted from a light emitting position, which component has a wavelength corresponding to a fluorescent light, a photoelectric converting means for converting the light, received through the filtering means, into an electric signal, a waveform shaping means for inverting and amplifying half of an output signal from the photoelectric converting means in synchronism with a timing displaced 90xc2x0 from an irradiating period of the light irradiating means, a low-pass filtering means for selectively extracting a direct current component from an output from the waveform shaping means, and a comparing means for comparing a detected voltage outputted from the low-pass filtering means with a predetermined voltage and for outputting a detection signal in the event that the detected voltage exceeds the predetermined voltage.
In order to accomplish the foregoing objects, the thirty-seventh invention provides an optical reading apparatus which comprises a projecting unit for projecting an exciting light necessary to excite a fluorescent substance onto a carrier formed with a fluorescent mark containing the fluorescent substance, a light receiving unit for receiving a fluorescent light emitted from the fluorescent substance and light reflected from the carrier and converting them into an electric signal, an amplifying unit for amplifying the electric signal outputted from the light receiving unit, and a signal detecting unit for detecting information recorded by the fluorescent mark from an output signal from the amplifying unit, which apparatus is characterized in that the amplifying unit has an amplification factor which is variable according to the intensity of the reflected light incident on the light receiving unit and in that the output signal from the amplifying unit which has a peak value lower than a predetermined value is supplied to the signal detecting unit for analog-to-digital conversion thereof to provide a digital signal corresponding to a pattern in which the fluorescent mark is formed.
In order to accomplish the foregoing objects, the thirty-eighth invention provides an optical reading apparatus which comprises a projecting unit for projecting an exciting light necessary to excite a fluorescent substance onto a carrier formed with a fluorescent mark containing the fluorescent substance, a light receiving unit for receiving a fluorescent light emitted from the fluorescent substance and light reflected from the carrier and converting them into an electric signal, an amplifying unit for amplifying the electric signal outputted from the light receiving unit, and a signal detecting unit for detecting information recorded by the fluorescent mark from an output signal from the amplifying unit, which apparatus is characterized in that the amplifying unit has an amplification factor which is variable according to the intensity of the reflected light incident on the light receiving unit and the intensity of the fluorescent light and in that the output signal from the amplifying unit which has a peak value lower than a predetermined value is supplied to the signal detecting unit for analog-to-digital conversion thereof to provide a digital signal corresponding to a pattern in which the fluorescent mark is formed.
In order to accomplish the foregoing objects, the thirty-ninth invention provides an optical reading apparatus which comprises a projecting unit for projecting an exciting light necessary to excite a fluorescent substance onto a carrier formed with a fluorescent mark containing the fluorescent substance, a light receiving unit for receiving a fluorescent light emitted from the fluorescent substance and light reflected from the carrier and converting them into an electric signal, an amplifying unit for amplifying the electric signal outputted from the light receiving unit, and a signal detecting unit for detecting information recorded by the fluorescent mark from an output signal from the amplifying unit, which apparatus is characterized in that the output signal from the amplifying unit is supplied to the signal detecting unit so that the output signal from the amplifying means can be sliced in the signal detecting unit by two or more slice signals having two or more slice levels to provide two or more digital signals whereby a digital signal corresponding to the fluorescent mark can be obtained by logically summing the two or more digital signals together.
In order to accomplish the foregoing objects, the fortieth invention provides an optical reading apparatus which comprises a projecting unit for projecting an exciting light necessary to excite a fluorescent substance onto a carrier formed with a fluorescent mark containing the fluorescent substance, a light receiving unit for receiving a fluorescent light emitted from the fluorescent substance and light reflected from the carrier and converting them into an electric signal, an amplifying unit for amplifying the electric signal outputted from the light receiving unit, and a signal detecting unit for detecting information recorded by the fluorescent mark from an output signal from the amplifying unit, which apparatus is characterized in that an output signal outputted from the amplifying unit when an amplification factor thereof is set to a low value and an output signal outputted from the amplifying unit when the amplification factor thereof is set to a high value are supplied to the signal detecting unit so that the output signals from the amplifying means can be sliced in the signal detecting unit by a slice signal having a particular slice level to provide two or more digital signals whereby a digital signal corresponding to the fluorescent mark can be obtained by logically summing the two or more digital signals together.
According to the first, ninth and fourteenth inventions described above, since the fluorescent substance is in the form of ultra-microparticles having an average particle size smaller than the wavelength of the fluorescent light of a maximum intensity emitted from the florescent substance and, in other words, since the wavelength of the fluorescent light is greater than the particle size of the fluorescent particles, the fluorescent light emitted from the fluorescent particles arrives at a surface of the fluorescent ink deposit having passed through the fluorescent particles positioned thereabove. Accordingly, the fluorescent light can be effectively radiated, detection of the fluorescent light is ensured, and the reliability can be increased.
According to the second, tenth and fifteenth inventions described above, since the fluorescent substance is in the form of ultra-microparticles having an average particle size smaller than the wavelength of the exciting light of a maximum intensity emitted from the florescent substance and, in other words, since the wavelength of the exciting light is greater than the particle size of the fluorescent particles, the exciting light can effectively irradiate the fluorescent particles in a lower region even though the fluorescent particles in an upper region exist above the lower region. Therefore, the efficiency of activation (excitation efficiency) of the fluorescent substance is high and, consequently, detection of the fluorescent light is ensured accompanied by an increase in reliability.
According to the third invention, the fluorescent substance comprises, as shown by the general formula (1) or (2), a salt of oxyacid containing, as an optical active element, one or more elements selected from the group consisting of Nd, Yb and Er. Even this fluorescent substance is in the form of microparticles and, therefore, detection of the fluorescent light is ensured accompanied by an increase in reliability.
According to the fourth invention, the fluorescent substance comprises, as shown by the general formula (3), (4) or (5), Fe and Er as an optical active element and at least one element selected from the group consisting of Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La.
Even this fluorescent substance is a novel fluorescent substance having a light emission spectrum different from that of the prior art fluorescent substance and is particularly suited for use in a field in which security is required.
According to the fifth invention, the fluorescent substance comprises, as shown by the general formula (6), (7) or (8), Yb as an optical active element and at least one element selected from the group consisting of Sc, Ga, Al, In, Y, Bi, Ce, Gd, Lu and La.
Even this fluorescent substance is a novel fluorescent substance having a light emission spectrum different from that of the prior art fluorescent substance and is particularly suited for use in a field in which security is required. Also, this fluorescent substance is in the form of generally spheroidal fluorescent particles of substantially uniform size with no acicular particles and can therefore be uniformly dispersed in a composition.
According to the sixth and eleventh inventions, the fluorescent substance containing at least one organic substance which contains a rare earth element selected from the group consisting of Nd, Yb and/or Er, and combined with at least one organic substance having at least one absorption band within the infrared region of light, such as, for example, polymethine, anthraquinone, dithiol metal, phthalocyanine, indophenol or azo dyestuff of a kind having at least one absorption band within the infrared region of rays of light. Therefore, the rare earth element has a fluorescent output sufficient for a high speed reading and can emit light in response to a variety of wavelength of the exciting light. In other words, in view of the fact that the wavelength of the exciting light varies depending on the rare earth element, the exciting wavelength (the wavelength of the exciting light required to excite the fluorescent substance) to be applied to the fluorescent substance can be varied advantageously.
In other words, although the fluorescent substance containing one or more elements selected from the group consisting of Nd, Yb and Er absorbs and emits light peculiar to the selected element or elements, the rare earth metal generally has a relatively low light absorption efficiency as compared with an organic compound and, therefore, addition of an organic compound having an absorption band within the infrared region of light is effective to increase the light absorption efficiency to thereby enhance the intensity of light emitted by the rare earth metal.
Also, in view of the fact that the wavelength of the exciting light varies depending on the rare earth element, the exciting wavelength to be applied to the fluorescent substance can be advantageously varied.
According to the seventh, twelfth and thirteenth inventions, the fluorescent substance contains, as shown by the general formula (9) or (10), at least one of Nb and Yb as an optical active element and, other than this optical active element, at least one oxide of Mo or W and an alkaline earth metal.
The reason that this fluorescent substance has an excellent water resistance appears as follows. Namely, while the water solubility depends on the magnitude of energies necessary to break the bond between anions and cations contained in the material to form a hydrate, that is, the magnitude of a bonding force between the anions and the cations, the bonding force is related to the valence and the coordination number of the ions. Accordingly, as compared with a salt having the same anions, the divalent alkaline earth metal exhibits a higher bonding force than the monovalent alkaline metal so far as the cations are concerned. Also, if, for example, MoO42xe2x88x92 is chosen for the anion, respective coordination numbers of Na and Ca are six and eight, and therefore, CaMoO4 exhibits a higher bonding force than Na2MoO4.
Accordingly, for the same anions, the use of the alkaline earth metal for the cations is advantageous in respect of the water resistance and this tendency appears to be maintained even where the rare earth element is added.
The eighth invention is characterized in that the flux material containing the salt expressed by T2RO4.nH2O is added with at least one optical active element selected from the group consisting of Nd and Yb, at least one oxide of one of Mo and W and an alkaline earth metal and is then calcinated, followed by dissolution of the flux material with a solvent to remove it.
With respect to the particle size of the fluorescent substance so prepared by the calcination referred to above, comparison of the prior art powdery fluorescent substance having a matrix comprised of Na2MoO4 and mechanically pulverized after the calcination, the powdery fluorescent substance of the present invention having a matrix of CaMoO4 and mechanically pulverized after the calcination and the fluorescent substance added with a water-soluble flux material during the calcination, but with the flux material having been removed by flushing subsequent to the calcination, have shown that, while the prior art substance was of a particle size of about 5 xcexcm at minimum, the substance of the present invention was found to be microparticles in which primary particles of a particle size within the range of about 2 to 5 xcexcm were secondarily aggregated, and the substance introduced with the flux material was found to be microparticles of a particle size not greater than 1 xcexcm.
In the solid phase reaction induced by the calcination the particle size of the starting material is one of factors that determine the particle size of a reaction product (in this case, the fluorescent substance). The smaller the particle size of the raw material, the smaller the particle size of the reaction product. Accordingly, the material of a particle size as small as possible should be chosen for the raw material.
Another one of the factors that determine the particle size of the fluorescent substance is the surface area of contact among the raw materials that induce the solid phase reaction. The larger the contact surface area, the more often the solid phase reaction occurs, resulting in acceleration of the particle growth. By way of example, considering the reaction of only the matrix comprised of CaMoO4 employed in the present invention, the solid phase reaction may be expressed by [CaCO3(s)+MoO3(s)xe2x86x92CaMoO4(s)+CO2(g)]. (In this case, the calcinating temperature is 750xc2x0 C. which is lower than the decomposition temperature, 900xc2x0 C., of CaCO3, but it is suspected that such a reaction, [CaCO3(s)xe2x86x92CaO(s)+CO3(g)], may occur as a result of somewhat decomposition.)
If for the flux material Na2MoO4 is employed which has a melting point at 687xc2x0 C. which is lower than the calcination temperature of 750xc2x0 C., the solid phase reaction takes place. CaCO3 and MoO3 are dispersed in the flux melt, accompanied by reduction in surface contact area among the raw materials. In view of this, the particle growth appears to be disturbed, resulting in reduction in particle size of the reaction product.
With respect to the light emission intensity, so long as the fluorescent substance added with and activated by, for example Nd and Yb is concerned, when emission outputs exhibited respectively by the conventional fluorescent substance containing Na2MoO4 as a matrix, the fluorescent substance of the present invention containing CaMoO4 as a matrix and the fluorescent substance having a particle size not greater than 1 xcexcm, as a result of excitation by the pulsating exciting light are compared, the fluorescent substance of the present invention has resulted in reduction of the light emission intensity down to about 80% of that exhibited by the conventional fluorescent substance and the fluorescent substance of the particle size not greater than 1 xcexcm has resulted in reduction of the light emission intensity down to about 40% of that exhibited by the conventional fluorescent substance.
However, when the sensitivity of an Si photodetector is taken into consideration, these emission intensities would bring about no problem in practice. This is because this reduction in emission intensity discussed above is attributable to the particle size of the fluorescent substance being smaller than that of the conventional fluorescent substance and not attributable to the type of matrix material.
The emission intensity and the response are associated with the transition probability of the rare earth element. Specifically, the higher the transition probability, the higher emission intensity and the higher the response. The optical transition of Nd and Yd which are used in the practice of the present invention as an optical active element is a transition of f-electrons between energy levels and is known as a forbidden transition in terms of the parity of the wave function.
However, in crystals, levels having a parity reverse to the f-trajectory due to the crystal field are mixed up and the fxe2x80x94f transition is permitted to a certain extent. This tolerance is large if the symmetric property of the crystal field is low and, hence, the transition probability is high. By way of example, while Na2MO4 employed in the conventional fluorescent substance is of a cubic system, CaMO4 employed in the practice of the present invention is of a pyramidal quadratic system and, therefore, the symmetric property of the crystal is low. Accordingly, in terms of material, the fluorescent substance of the present invention cannot be considered inferior to the conventional fluorescent substance in respect of the emission intensity and the response.
Also, the response does not depend on the particle size, and the fluorescent substance of the present invention which is considered having a high transition probability exhibits a somewhat higher response.
According to the sixteenth invention, since the content of the fluorescent particles in the fluorescent ink deposit formed by printing is greater than 1 wt %, but smaller than 30 wt %, the presence of the ink deposit is not noticeable in sight and, therefore, the ink deposit will not adversely affect the appearance of the fluorescent mark carrier. Accordingly, it is suited for the fluorescent mark carrier to have a security.
According to the seventeenth invention, since the fluorescent ink deposit formed by printing has a thickness not greater than 35 times the particle size of the fluorescent particles, the presence of the ink deposit is not noticeable in sight and, therefore, the ink deposit will not adversely affect the appearance of the fluorescent mark carrier. Accordingly, it is suited for the fluorescent mark carrier to have a security.
According to the fluorescent composition of the eighteenth invention, since the binder for dispersing and retaining the fluorescent microparticles has a light transmissivity with respect to each of the exciting and fluorescent light being not lower than 80%, entry of the exciting light into the fluorescent ink deposit and exit of the fluorescent light generated internally of the fluorescent ink deposit to the outside take place efficiently. Because of this, assured detection of the fluorescent light is possible, accompanied by increase in reliability.
According to the fluorescent mark carrier of the nineteenth invention, the fluorescent particles in the fluorescent mark carrier are deposited on a fiber aggregation having minute surface irregularities such as, for example, paper, and therefore the fluorescent ink deposit has a surface formed with corresponding minute surface irregularities. If the fluorescent ink deposit containing the fluorescent particles are formed on a smooth surface such as, for example, a synthetic film, the surface of the ink deposit will become smooth. If this smooth surface of the fluorescent ink deposit is irradiated with the exciting light, portion of the exciting light will undergo a regular reflection and will no longer activate the fluorescent substance. However, deposition of the fluorescent particles on the fiber aggregation such as accomplished in the present invention is effective to substantially eliminate such a regular reflection of the exciting light and, therefore, the efficiency of excitation of the fluorescent substance is high.
According to the fluorescent mark carrier of the twentieth invention, since the fluorescent ink deposit in the fluorescent mark carrier has a 20% or lower visible ray absorption characteristic, the fluorescent ink deposit is substantially colorless and transparent and, for this reason, it will not adversely affect the appearance of the fluorescent mark carrier and is suited for use where security is of great importance.
According to the optical reading apparatus of the twenty-first invention, the mirror has a portion thereof provided with a light transmitting region for allowing a substantially entire quantity of the exciting light from the light emitting element to pass therethrough. Therefore, as compared with the semitransparent mirror employed in the conventional optical reading apparatus, the quantity of the exciting light used to irradiate the fluorescent substance can be increased, with activation of the fluorescent substance enhanced effectively.
Moreover, the quantity of the fluorescent light reflected by the mirror is relatively large as compared with that reflected by the semitransparent mirror. For this reason, detection of the fluorescent light is ensured and the reliability can be increased.
According to the optical reading apparatus of the twenty-second invention, since the pattern of the exciting light emitted from the light emitting element is elliptical with its major axis extending in a direction lengthwise of the bar code, the area of the illuminated surface increased as compared with the conventional round pattern of the exciting light (that is, assuming that the diameter of the round pattern is equal to the length of the minor axis of the elliptical pattern). For this reason, the intensity of the light emitted is high, making it possible to accomplish an assured detection of the fluorescent light accompanied by increase in reliability.
With the optical reading apparatus of the twenty-third invention, since the velocity v of transport of the fluorescent mark carrier is regulated by the relationship between the length d of the opening in the slit member and the rise time tu, only the information desired to be read (for example, a single bar code) can be assuredly read out with no time wasted. For this reason, the reliability in reading can be increased, making it possible to accomplish a high speed reading.
With the optical reading apparatus of the twenty-fourth invention, since the velocity v of transport of the fluorescent mark carrier is regulated by the relationship the interval between neighboring portions printed with the fluorescent substance and the fall time td, only the information desired to be read can be assuredly read out with no possibility of being adversely affected by the fluorescent afterglow from the neighboring bar and, therefore, the reliability can be increased.
In the optical reading apparatus according to the twenty-fifth invention, the provision is made of the slit member between the second convex lens and the light receiving element wherefore, even though the thickness of the fluorescent mark carrier caries to a certain extent, the fluorescent mark carrier can be satisfactorily transported without damaging the slit member.
According to the twenty-sixth invention, the semiconductor laser diode having an excellent light collecting ability and also an excellent light directivity is employed for the light emitting element and, for the drive circuit for driving the semiconductor laser diode, the circuit having an automatic power control function so that the exciting light is monitored to control output conditions of the exciting light being emitted from the laser diode. Therefore, both of the pulse interval and the pulse intensity of the exciting light are fixed to make it possible to provide the optical reading apparatus stabilized in operation.
According to the twenty-seventh invention, since the relationship among the velocity v of transport of the fluorescent mark carrier, the length d of the opening in the slit member and the rise time tu are uniquely defined, it is possible to provide a high speed reading system capable of reading out only the information desired to be read with no time wasted.
According to the twenty-ninth invention, since the relationship among the velocity v of transport of the fluorescent mark carrier, the interval L between neighboring portions printed with the fluorescent substance and the fall time td is uniquely defined, it is possible to provide a highly reliable reading system capable of reading only the information desired to be read with no possibility of being adversely affected by the fluorescent afterglow from the neighboring bar.
Since each of the twenty-ninth and thirty inventions is so constructed as hereinbefore described, a merchandise sorting can be automatically, efficiently and assuredly accomplished.
According to each of the thirty-first and thirty-second inventions, since the lead-in area of the fluorescent mark has a length sufficiently greater than the longest continuous portion of the pattern formed at the data area, the intensity of the fluorescent light emitted from that lead-in area is higher and more stabilized than the data area and is comparable to the intensity proper to particular detecting condition or environments.
Moreover, since that lead-in area is defined at a location adjacent a portion of the data area which is first scanned and is continued to the data area, that lead-in area works together with the data area so as to provide a substantially constant contrast over the entire region of the data area and the intensity of the fluorescent light emitted from the data area can vary uniformly over the entire region of the data area.
Therefore, by initially detecting the intensity of the fluorescent light at the lead-in area and then comparing the intensity of the fluorescent light emitted from the data area with a reference value represented by the intensity of the fluorescent light from the lead-in area, the contents of the mark formed at the data area can advantageously be determined accurately.
In the optical reading apparatus according to each of the thirty-third and thirty-fourth inventions, when the mark is irradiated by the light from the light irradiating means, not only does the mark reflect the incoming light, but also an irradiated portion of the mark emits the fluorescent light of a particular wavelength. The incident light containing the reflected component and the fluorescent component is passed through the optical filtering means to selectively extract the light of a wavelength equal to that of the fluorescent length and is subsequently converted into an electric signal by the photoelectric converting means so that the electric signal can be processed by the waveform detecting means.
In the waveform detecting means, the magnitude of the amplitude of the incident and the intensity of the fluorescent light are detected individually. Therefore, by preparing a comparison value which varies with change in intensity of the incident light and allowing the mark determining means in the subsequent stage to compare the detected value with the comparison value, the comparison value can be automatically set to an optimum value according to change in intensity of the incident light itself.
Moreover, by allowing a signal input determining means to determine at all times the intensity of the incident light and to initiate a determining operation only when the significant incident light is detected, only genuine data are used as a detected value and a comparison value and, therefore, the reliability can be increased advantageously.
In the optical reading apparatus according to each of the thirty-fifth and thirty-sixth invention, when the pulsating light from the light irradiating means is projected onto the mark at a predetermined timing, light from that portion of the mark on which the light impinges enters the optical filtering means. The light incident on the optical filtering means contains external light having a random distribution of wavelength, but having an intensity of a substantially constant level, reflected light having a distribution of wavelength that can be specified, but having an intensity that varies in a fashion represented by a rectangular wavelength, and fluorescent light having a particular wavelength different from that of the reflected light, but having a intensity that varies with irradiation of the light.
Therefore, the use of the optical filtering means is effective to selectively pass the light of a wavelength equal to that of the fluorescent light therethrough so that the other light components than the fluorescent light can be attenuated down to a value as small as possible, thereby making it possible for the photoelectric converting means to convert the intensity of the light into an electric signal of a magnitude proportional to such intensity of the light.
While the external light has a substantially constant intensity, the reflected light has a cyclically varying intensity of a substantially constant level. On the other hand, the fluorescent light has an intensity that varies according to the irradiating light at the same timing as the reflected light. In other words, the fluorescent light just emitted and the fluorescent afterglow attain a maximum intensity when the irradiating light is switched off, and a minimum intensity when the irradiating light is switched on.
Accordingly, if the waveform shaping means is so designed so as to invert and amplify the input signal, inputted during a period of irradiation, at a timing shifted 90xc2x0 relative to the period of irradiation, the half period during which both of the emitted light and the fluorescent afterglow are relatively high can be obtained in the form of a change in positive voltage whereas the half period during which they are relatively low can be obtained in the form of a change in negative voltage.
In the meantime, while each of the external light and the reflected light gives rise to positive and negative voltages that are equal to each other, the electric signal indicative of the fluorescent light is so inverted that the difference between the both can be maximized. Accordingly, when the electric signal is passed through the low-pass filtering means in the subsequent stage, both of the external light and the reflected light are cancelled, but the fluorescent light if contained gives rise to the difference between the positive and negative signals which is extracted as a direct current voltage. Therefore, if it is determined that the difference between the direct current voltage with a preset value set in a comparator is significant, a mark signal indicative of the position of the mark is outputted.
In the optical reading apparatus according to any one of the thirty-seventh to fortieth inventions, the level and amplitude of the analog reproduction signal vary considerably depending on surface properties of the carrier on which the fluorescent mark is formed. On the other hand, the level and amplitude of this analog reproduction signal can be properly adjusted by varying the amplification factor of the amplifying unit. In view of this, if the amplification factor of the amplifying unit can be switched depending on the intensity of the reflected light incident upon a light receiving unit and the level of the analog reproduction signal is matched with a predetermined slice signal level set in the signal detecting unit, a desired binary signal can be obtained with a slice signal of a predetermined level regardless of the properties of the carrier and, therefore, information associated with the fluorescent marks on the carriers of a varying material can be precisely read out with the single reading apparatus.
Also, if the amplification factor of the amplifying unit is adjustable to one of different values depending on the intensity of the reflected light and that of the fluorescent light both incident upon the light receiving unit, it is possible to match the level of the analog reproduction signal with that of the slice signal as accurately as possible and, therefore, the reading of the fluorescent mark signal can be accomplished highly precisely.
On the other hand, where the analog reproduction signal detected from a series of fluorescent marks formed on one and the same carrier varies in level, no accurate reading of the fluorescent mark information is possible with the previously described first and second means. Accordingly, if the analog reproduction signal supplied to the signal detecting unit is sliced by two or more slide signals having two or more slice levels appropriate to the level variation, the binary signal of the analog reproduction signal for each level can be obtained. If a logical sum of the binary signals for those levels is calculated, the binary signal corresponding to the entire analog reproduction signal can be obtained. Thus, even though the analog reproduction signal detected of the series of the fluorescent marks formed on one and the same carrier accompanies a partial level variation, the fluorescent mark information can be read out accurately.
Also, in a similar situation, even if without the analog reproduction signal being sliced by the two or more slice signals, the amplification factor is adjusted according to each of the levels of the analog reproduction signals so that the analog reproduction signal can be sliced by a slice signal having a particular slice level, the binary signals of the analog reproduction signals for those levels can be obtained. Even in this case, if a logical sum of the binary signals for those levels is calculated, the binary signal corresponding to the entire analog reproduction signal can be obtained.
By way of example, with respect to the analog reproduction signal of a high level, this analog reproduction signal is sliced by a particular slice signal with the amplification factor lowered. At this time, no digitization takes place of the analog reproduction signal of a low level. On the other hand, with respect to the analog reproduction signal of the low level, this analog reproduction signal is sliced by the particular slice signal with the amplification factor increased. At this time, no digitization takes place of the analog reproduction signal of the high level. Accordingly, by taking the logical sum of these binary signals, the binary signal corresponding to the entire analog reproduction signal can be obtained.